When emailing external parties, it is a good idea to CC the other colleagues within your organization that may have an interest in the email. Some of the benefits of CC'ing others are:
Note: Don't cc people unnecessarily - it is another email problem!
Some people might reply only to the sender of the email ('little r'), ignoring the fact that there were other persons included in the original email. Obviously the original sender intended to keep everyone in the loop, so it would be polite to CC everyone included on the original communication ('Reply All').
✅ Figure: Good example - 'Reply All' so that everyone is kept in the loop
Sometimes the other person will 'little r' instead of 'Reply All' by mistake. This can be problematic as those dropped off the loop are needed as part of the decision making.
If you are still on the loop, you should reply to the thread as soon as possible, adding back all those dropped from the loop.
❌ Figure: Bad example - 'Little r' should be rarely clicked
✅ Figure: Good example - Adding back those incorrectly dropped from the loop
Video: Top 10+ Rules to Better Email Communication with Ulysses Maclaren